Continuous casting of plates and strips from non-ferrous metals



ROUS METALS Sept. 21, 1965 E. HERRMANN CONTINUOUS CASTING OF PLATES AND STRIPS FROM NON-FER Filed Aug. 21, 1962 INVENTOR: ERHARD HERRMANN,

HIS ATTOR/VEX United States Patent Ltd.)

Filed Aug. 21, 1962, Ser. No. 227,622 Claims priority, application Switzerland, Aug. 25, 1961, 9,926/61 4 Claims. (Cl. 22-573) In the continuous casting of plates and strips of relatively thin section in which the width exceeds from to times the thickness, but especially of still more slender plates having a thickness of for example 20 mm. and a width of 500 to 1000 mm., there arise difiiculties during solidification which are not encountered in the continuous casting of rollings slabs, round billets or other similar pieces of a heavy section. The cooling of the melt in the mold is of course much easier with slender sections than with heavy ones because ofthe greater surface of the molten metal relatively to its volume, but on the other hand there is the danger of tension cracks in the longitudinal axis of the casting due to the fact that solidification begins at the edges and proceeds to the middle of the casting where the shrinkage cannot be compensated as the solidified edges do not yield. These conditions during solidification are possibly one of the causes for the necessity of limiting the maximum width of the cast strips when casting between a rotating wheel and a covering strip in the so called rotary-casting equipments, whereas in casting between two rolls according to the well known process of the Hunter Engineering Company there is no such limitation. It is assumed that with the latter process strips up to a width of 1500 mm. and a thickness of 6.4 to 13 mm. can be cast without longitudinal cracks appearing in the middle because the metal solidifies mostly before reaching the narrowest passage between the two rolls (the nip of the rolls), so that after the main solidification a squeezing of the pasty metal takes place which squeezing counteracts the shrinkage.

The object of my present invention is a method for the continuous casting of thin plates or strips from non-ferrous metals according to which method the formation of longitudinal cracks in the middle of the casting is avoided by means of a novel control of the dissipation of heat.

According to my invention the cooling of the cast metal in the mold is controlled in such a way that the middle part of the solidification front, considered in the width of the casting, projects in opposite direction to the metal flow, that means in direction to the mold inlet. This may, for instance, be accomplished by the specific form of the mold and coupled, for example, with spraying-cooling of the center portion of the casting, or heating of the edge portions. Thereby the beginning of the cooling is transferred substantially to the middle of the casting, so that just after the beginning of the solidification solid metal forms the middle of the casting whereas at both sides of the middle solid zone the metal is still liquid.

In the known art the conditions during solidification are just reverse as well in the normal DC. or full continuous casting of heavy sections as in the continuous casting of thin plates and strips. In some cases in the casting of rolling slabs a very flat solidification front is aimed at, but never a fully plane front has been attained and in no case an inversion of the solidification front, that means a projeciton of the middle part of the solidification front in opposite direction to the metal flow.

The method according to my invention is not applicable to the casting of heavy sections, for example rolling slabs and round billets as it is not possible to dissipate the heat in the middle of the casting in such a way that the solidification front projects into the liquid metal pool. By using a ring of small height as casting mold one can obtain at the utmost that the molten metal pool becomes shallow and the solidification front approaches the shape of a plane. The method of the invention is only applicable in the casting of thin strips or plates because in this case the cooling takes place substantially in two dimensions and because the projection of the solidification front in opposite direction to the metal flow is essential only in the width of the casting. The shrinkage in transverse direction to the width of the plate or strip is not important in view of avoiding longitudinal cracks in the middle of the casting. Only a great width of the plate or strip relatively to its thickness makes possible the performance of the method according to the invention.

When using metallic molds which are attacked by the molten metal, it is of course necessary that also at the narrow sides the metal solidifies at once after its entrance in the mold in order to protect the wall of the mold, in case it is not otherwise protected by a coating. But the frozen shell at the narrow sides must be thin until it passes on its way to the outlet of the mold the plane to which the middle part of the solidification front projects; only then the shell may grow rapidly in direction to the middle of the casting where it reaches the central solidification zone and combines with it.

As liquid metal is present on both sides of the projection of the solidification front, the latter can suck liquid metal during the solidification shrinkage and the further shrinkage, whereby dangerous internal tensions leading to longitudinal cracks in the middle of the casting are avoided.

The most suitable shape and length of the projecting middle solidification front depends on many factors, for instance on the casting material, the material of the mold, the casting section, the temperature, the casting speed and so on. In some cases a projection of the solidification front by a length of 5% of the width of the plate or strip may be sufficient, but mostly a greater projection, for instance of 15 to 30%, is necessary. The maximum length of the projection is only limited by the length or height of the mold. Preferably the most suitable shape of the solidification front is determined by casting experiments.

The invention is further described by means of the accompanying drawing in which FIG. 1 is a fragmentary vertical sectional view of a vertical continuous casting mold and casting, taken on the line 1-1 of FIG. la;

FIG. la is a fragmentary perspective view thereof;

FIG. lb is an end elevational view of the same;

FIG. 2 is a side elevational view of the mold;

FIG. 3 is a side elevational view, similar to FIG. 2, but embodying a further modification;

FIG. 4 is a side elevational view, similar to FIGS. 2 and 3, but embodying a further modification;

FIG. 5 is a fragmentary elevational View of a modification embodying a casting wheel; and

FIG. 6 is a perspective view of the casting wheel of FIG. 5.

In carrying the invention into effect, and referring now to FIGS. 1, 1a and 1b, in the mold l a strip 2 is shown during casting; the strip is shown in a section through the narrow sides of the mold and of the casting. The arrow a indicates the direction of the metal filow 3 in the molten metal pool. The middle part 4 of the solidification front projects in opposite direction to the metal flow. 5 indicates the frozen shell which is formed at the narrow sides of the mold at once after pouring the metal into the a mold. Of course also at the broadsides on both sides of the projection of the solidification front a frozen shell is formed which must be held as thin as possible until it passes the plane 6 of the projecting part 4 of the solidification front. Only at 7 is the strip solidified throughout its section.

In graphite molds the formation of a frozen shell at the entrance of the mold may be avoided if non-ferrous metals are cast.

For performing the method according to the invention in the vertical semi-continuous casting a mold may be used in which the narrow sides 8 reach lower than the middle part of the broad sides 9, as sketched in FIG. 2, which shows schematically a side view of the mold. The narrow sides 8 and the adjacent parts of the mold 1 are longer than the middle part of the broad sides 9 which are cut out at 10. Other possible shapes of the broad sides 9 of a mold are shown in FIGS. 3 and 4. Due to the great recess 10 at the broad sides 9 of the mold, cooling water may be sprayed for instance from nozzles 16 onto the casting in such a way that solidification preferably takes place in the middle part of the casting considered from the broad side. This effect may be increased by a thermal insulation of the narrow sides of the mold, for example by means of asbestos plates. The mold may also be assembled in such a way that the narrow sides 8 consist of a material (for example graphite), which is not such a good thermal conductor as the material of the broad sides 9 or the middle part of them, which material may be copper. Also heating the upper part of the narrow sides of the mold can be taken into consideration.

The invention may also be used in the vertical multiple continuous casting where simultaneously several castings are produced. But in this case the cooling of the broad sides presents greater difliculties.

The method according to the invention is especially suitable for the horizontal continuous casting in which the casting mold is joined tightly to a supply container filled with the molten metal, so that there is no free molten metal level in the casting mold. Such a horizontal casting process is disclosed for instance in the US. Patent 2,996,771 and in the British Patent 806,313. In the horizontal continuous casting process thin plates are cast preferably in flat position and not upright in order that the cooling is the same at both narrow sides. When applying the method according to my invention to the horizontal continuous casting, it is also preferable with regard to the slender section to hold the melt flowing into the mold under a relatively high pressure, which can be attained easily by maintaining a high metal level in the supply container.

The method according to my invention may also be applied in the strip casting between a rotating casting Wheel and a covering strip (rotary method). In the simplest way the casting wheel comprises a middle ring made from a metal of high thermal conductivity, for example aluminum but preferably copper, which ring may be provided at its inner circumference with cooling ribs, and of two side parts made from a metal of a relatively low thermal conductivity, suitably from steel. FIG. 5 shows schematically and not true to size the front elevation of the upper part of such a casting wheel, consisting of a ring 11 made from copper and two side parts 12 and 13 made from steel. 14 designates the covering steel strip and 15 the casting mold. The assembling of the ring with the side parts may be performed by mechanical means or by welding or brazing. Copper has a thermal conductivity which is five times that of steel. In the described casting wheel the main part of the heat is removed through the copper ring 11 which is cooled at its inner circumference with water, which results in the formation of a solidification front having a middle portion thereof projecting beyond the portions adjacent thereto in a direction opposite to the direction of metal flow. When casting relatively thick strips it is not necessary to take special precautions with regard to the cooling of the covering strip; but when casting specially thin strips it may be advantageous to begin the cooling of the covering strip with spray water only behind the place where the metal enters the mold.

What I claim is:

l. A method for the continuous casting of plates and strips from non-ferrous metals having a width of from 15 to 20 times the thickness according to which method the cooling in the casting mold that has wide and narrow sides is controlled so as to produce a solidification front extending upwardly at the narrow sides of the mold thence downwardly adjacent both sides of the solidified sides and thence upwardly for at least five percent of the width of the castings in a direction opposite to the direction of fiow of the metal. 3

2. A method for the vertical, semi-continuous casting according to claim 1, said casting having opposite broa-d sides and narrow sides, wherein the middle part of the broad sides of the originating casting are cooled more vigorously than the zone adjacent the middle part.

3. A method for the strip casting between a rotating casting wheel having central circumferential part and side parts and a covering strip according to claim 1, according to which method the central circumferential part of the casting wheel is cooled more vigorously than the side parts of the casting wheel.

4. An apparatus for strip casting comprising a rotating wheel having a middle circumferential part and side parts and a covering strip, between which there is formed the casting mold, said middle circumferential part of said casting wheel being made from copper and said side parts from steel.

References Cited by the Examiner UNITED STATES PATENTS 2,450,428 10/48 Hazelett 22-200.l X

MARCUS U. LYONS, Primary Examiner. MICHAEL V. BRINDISI, Examiner. 

1. A METHOD FOR THE CONTINUOUS CASTING OF PLATES AND STRIPS FROM NON-FERROUS METALS HAVING A WIDTH OF FROM 15 TO 20 TTIME THE THICKNESS ACCORDING TTO WHICH METHOD THE COOLING IN THE EASTING MOLD THAT HAS WIDE AND NARROW SIDES IS CONTROLLED SO AS TO PRODUCE A SOLIDIFICATION FRONT EXTENDING UPWARDLY AT THE NARROW SIDES OF THE MOLD THENCE DOWNWARDLY ADJACENT BOTH SIDES OF THE SOLIDIFIED SIDES AND THENCE UPWARDLY FOR AT LEAST FIVE PERCENT OF THE WIDTH OF THE CASTINGS IN A DIRECTION OPPOSITE TO THE DIRECTION OF FLOW OF THE METAL. 